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The work reports different forms of solid solution ordering: from the well-known atom redistribution processes over positions and the decomposition of the solid solution to the formation of superstructures, modulated structures, rotation of atomic groups, splitting of sites. For each ordering form as a crystal chemical phenomenon the position of atoms, molecules, and vacancies in the crystal structure of the solid solution is considered and the place of these processes among the main crystal chemical phenomena is determined. The manifestation of order-disorder processes in phase diagrams of systems is also analyzed: from the classical heterogeneous decomposition of solid solutions to the formation of ordered chemical compounds and other phase transitions. The necessity of a thorough study of the atomic-molecular nature of the solid solution ordering by modern X-ray diffraction crystallographic methods and high-resolution electron microscopy is demonstrated. For each ordering form examples are given, the driving force of the process is distinguished, and a brief literature review is presented.

The molecular dynamics method is used to study liquid aqueous solutions of helium and neon, liquid water films and solid films with an ice II structure in helium and neon atmospheres, and solid solutions of helium and neon in ice II. Gas atoms wander randomly in water and make occasional slow jumps. The structure of the hydrate shell of the gas atoms bears little resemblance to the structure of ice II and other ice modifications. The solubility of neon in a water film is only a little higher than that of helium. Helium and neon atoms that find themselves in the channels of a thin ice II film make the same jumps along the channels as those along the channels in the structure of ice II crystals. The motions of two neon atoms in the neighboring (along the z axis) planes are correlated, whereas there is no correlation between the motions of helium atoms.

The solvent effects on the NH stretching of 1-(4-pyridyl)piperazine (1-4pypp, C₉H₁₃N₃) are investigated by density functional theory (DFT). The B3LYP hybrid density functional is used with the 6-311+G(3df,p) basis set in the polarizable continuum model (PCM). Computations are performed with 18 different polar or non-polar solvents. The calculated frequencies of the solvent-induced NH stretching vibrations are correlated with some solvent parameters such as the Kirkwood-Bauer-Magat (KBM) equation, the solvent acceptor number (AN), Swain parameters, and the linear solvation energy relationships (LSER). The present work explores the effects of the medium on the n(NH) vibrations. The findings of this research can be useful for piperazines.

The C₂₀ (cage), C₂₀ (bowl), C₂₀H₁₀ (bowl) fullerene structures and their nitrogen doped derivatives such as C₂₀NH (cage), C₂₀NH (bowl), C₂₀H₁₀N (bowl), C₂₀H₁₀NH (bowl) are fully optimized at the MPW1PW91/6-31G level of theory. The natural atomic charge comparison shows that in C₂₀H₁₀N (bowl), the nitrogen atom with about -0.58 has a more negative charge with respect to other nitrogen doped structures. The nuclear magnetic resonance chemical shielding is evaluated for nitrogen doped structures and the neighbors connected to nitrogen, C₆, and C₇ atoms. The nitrogen atom doped on carbon sites of C₂₀H₁₀N (bowl) has the largest shielding isotropic shifts to the upper field (-203.58 ppm). This means that the electron density around nitrogen in the C₂₀H₁₀N (bowl) structure is higher. Interestingly, there is a significant correlation between the charges and s_iso values of nitrogen and carbon atoms (C₆ and C₇). Namely, as the charge becomes more negative, s_iso shifts to the upper field. It is predicted that nitrogen doped C₂₀H₁₀N (bowl) with the maximum electron density adopts this structure for electrophilic reactions.

Zinc halide complexes of thionicotinamide (TNA) having the general formula [Zn(TNA)₂X₂] (X = Cl^-, Br^-, I^-) are prepared and characterized by thermal analysis, IR and NMR spectroscopy. The crystal structure of one of them, dichloridobis(thionicotinamide-kN)zinc(II), [Zn(TNA)₂Cl₂] (1), is determined using X-ray crystallography. In 1, the zinc atom is coordinated by two thionicotinamide ligands through nitrogen atoms and two chloride ions in a distorted tetrahedral coordination environment. The molecular structure of the complex is stabilized through intermolecular hydrogen bonding.

Voltaite of the composition [K_0.90(NH₄)_0.10]₂(Fe_3,190²⁺Fe_1,124³⁺Mg_1,686)(Fe_0,938³⁺Mg_0,062)₂(Al_0,98Fe_0,02³⁺)×(SO₄)₁₂x18.9H₂O is obtained by treating a polymetallic sample with sulfuric acid. The crystal structure of the substance is formed of (Fe³⁺,Mg)O₆ and (Fe²⁺,Fe³⁺,Mg)O₄(H₂O)₂ octahedra and a (K⁺,NH₄⁺)O₁₂x12-vertex polyhedron arranged in a three-dimensional framework due to the bridging function of the SO₄^2- ion. In the framework voids, [(Fe³⁺,Al)(H₂O)₆]³⁺ cations with aqua ligands disordered over several positions are located.

A new complex [Cu₂(L)₄(DMF)₂] (1) with benzoic acid (HL) as a ligand is synthesized by the solid phase synthesis method. Crystal data for the complex are as follows: monoclinic, space group P2₁/n, a = 10.593(2) Å, b = 10.123(2) Å, c = 16.336(3) Å, β = 93.55(3)°, V = 1748.4(6) ų, D_c = 1.439 g/cm^-3, Z = 4, F (000) = 780, GOOF = 1.003, final discrepancy factors R₁ = 0.0624, wR₂ = 0.1559. In 1, the Cu(II) ion is coordinated by six atoms to give a distorted octahedral coordination geometry. The electrochemical, fluorescent, and magnetic properties of 1 are studied. The results show that the electron transfer of 1 is quasi reversible in the electrode reaction corresponding to Cu(II)/Cu(I), and 1 exhibits three relatively strong fluorescent emission peaks at 403, 425, and 454 nm. In addition, complex 1 displays the antiferromagnetic property in a temperature range of 300 ~ 10 K.

A new mixed-ligand copper(II) complex of 1,10-phenanthroline and nitrate ligands [Cu(C₁₂H₈N₂)(NO₃)₂] _n is prepared and its crystal structure is determined by X-ray diffraction. The complex crystallizes in the monoclinic space group P21/n, with unit cell dimensions a = 8.8226(3) Å, b = 9.1462(1) Å, c = 17.2507(4) Å, β = 101.680(2)°, Z = 4, V = 1363.19(6) ų. The crystal structure is solved by the Patterson method and refined by full-matrix least squares treatment on F ² to final values R1 = 0.0447 and wR2 = 0.1053. The Cu^II ions are five-coordinated in a CuO₃N₂ environment, giving a distorted square-based pyramidal geometry. The Cu…Cu distance in the [Cu(C₁₂H₈N₂)(NO₃)₂] _n zigzag polymeric chain is 5.258(1) Å. The structure of the title compound is polymeric and consists of layers running parallel to (101), interconnected by π-π interactions, strong enough to form a three-dimensional framework with tunnels along the a axis.

Two iridium acetylacetonate complexes bearing axial bromide-substituted pyridine (3-bromopyridine, 1 and 4-bromopyridine, 2) are synthesized and their crystal structures are determined by single crystal X-ray diffraction. In both complexes, a distorted octahedral geometry of the central Ir(III) atom is formed by four oxygen atoms of two acetylacetone ligands, a carbon atom of one acetylacetone ligand, and a nitrogen atom of bromide-substituted pyridine.

Rhenium-molybdenum cluster compounds K_5.3Rb_0.7[Re₃Mo₃S₈(CN)₅] (1) and K_4.4Cs_1.6[Re₃Mo₃S₈(CN)₅] (2) are obtained by the interaction of an equimolar mixture of ReS₂ and MoS₂ with molten KCN and RbI/CsCl, respectively. The structure of the complexes is determined by the XRD method. The compounds crystallize in the tetragonal crystal system, space group I4/m. The crystal structure is composed of anionic chains of [Re₃Mo₃S₈(CN)₄(CN)_2/2]^6- aligned along the a crystallographic axis and M⁺ cations located in voids of the lattice. The effect of additional Cs⁺ and Rb⁺ cations on the crystallographic parameters and geometric characteristics of the clusters is analyzed.